defaultdict使用及__missing__理解

import collections
import re
WORD_RE = re.compile(r'w+')
index = collections.defaultdict(list) #用list方法作为默认工厂创建一个默认字典
with open('xx.txt',encoding='utf-8') as fp:
for line_no,line in enumerate(fp,1):
for match in WORD_RE.findeiter(line):
word = match.group()
column_no = match.start()+1
location = (line_no,column_no)
index[word].append(location) # 如果index没有Word记录，会调用默认工厂，创建一个空列表
for word in sorted(index,key=str.upper):
print(word,index[word])

 

import collections
class StrKeyDict(collections.UserDict):
def __missing__(self,key):
if isinstance(key,str):
raise KeyError(key)
return self[str(key)]
def __contains__(self,key):
return str(key) in self.data
def __setitem__(self,key,item):
self.data[str(key)] = item

 不可变映射类型

import collections
from types import MappingProxyType
d = {1:'A'}
d_proxy = MappingProxyType(d)
d_proxy[1] # A
d_proxy[2] #报错因为不可变
d_proxy[2] = 'B' #{1:'A',2:'B'}